Layers of rainforest
The Amazon rainforest is the most biodiverse region on Earth. There are thousands of tree species, most of which grow to between 24 and 30 metres tall, developing huge networks of branches that make up the canopy layer. A few trees grow even taller and poke up above the canopy, forming the emergent layer – small flying and gliding animals like birds, bats, and butterflies are good at manoeuvring from tree to tree up where it’s windy. Below the main tree canopy, the understory layer is darker and stiller. Plants growing there often have extravagant, very fragrant flowers in order to attract pollinators without a lot of light. The forest floor layer is even darker, and few plants grow there.
The most active part of the rainforest is the canopy layer, which is the six or so metres of treetops that essentially form the roof of the ecosystem 24 metres above the ground. More animals live in the canopy than in any other layer – birds including macaws and toucans, monkeys, spiders, sloths, and hundreds of thousands of insects – that eat the fruits and leaves of trees and sleep in the branches.
Although there are places in the Amazon where the tree canopy is so thick that no light reaches the ground, there are other spots where humans (and there are a lot of them there) are farming, ranching, and engaging in other activities that change the landscape. Clear-cutting in recent years has revealed evidence of land use by earlier groups as well: 2000-year-old huge geometric earthworks form squares and circles that stretch as far as a city block. Some trenches are 3.5 wide and 4 metres deep. Researchers aren’t sure what the geoglyphs were used for, but a recent study in The Proceedings of the National Academy of Sciences found that ancient humans actively managed the forest using sustainable practices. “New estimates for the population of Amazonia in pre-colonial times range between 6 and 10 million people, which is many more than today,” says Jennifer Watling, an archaeologist who led the study. “These people had many ingenious ways of making the forest more productive without damaging it for future generations.”